Electric eels – cool animals, for sure. What makes them cool is their ability to produce an alarming amount of electricity outside of their bodies, but how do they do it? For years, scientists were unsure, but that’s all changed. Thanks to researchers from Michigan State University, University of Wisconsin-Madison, University of Texas-Austin and the Systemix Institute, the electric eel genome has been sequenced for the first time. It revealed not just the mechanics of the electric eel, but all fish that produce external electricity.

“It’s truly exciting to find that complex structures like the electric organ, which evolved completely independently in six groups of fish, seem to share the same genetic toolkit,” said Jason Gallant, MSU zoologist and co-lead author of the paper. “Biologists are starting to learn, using genomics, that evolution makes similar structures from the same starting materials, even if the organisms aren’t even that closely related.”

All told, the electric genome has evolved six times in the history of life, one for each lineage of electric fish. Even Charles Darwin cited such animals as examples of convergent evolution. While all muscles technically produce electricity by contracting, certain fish began to really ramp things up between 100 and 200 million years ago. They evolved electrolytes from their muscle cells, organized in sequence and capable of generating much higher voltages than those used to make muscles work in the conventional way.

To imagine the sequencing, think of the way batteries are aligned in a flashlight. An eels body contains millions of these, all working together to fire an electric discharge of higher voltage than a standard household electrical outlet.

“Evolution has removed the ability of muscle cells to contract and changed the distribution of proteins in the cell membrane; now all electrocytes do is push ions across a membrane to create a massive flow of positive charge,” said Lindsay Traeger, U-W graduate student and co-author of the study.